Solvent-based paint removers have achieved popularity and widespread use because of their ability to easily remove fully or partially-cured coatings from substrates. Methylene chloride and other chlorinated hydrocarbons have been popular because of their effectiveness and low cost. Methylene chloride, however, is highly toxic and a suspected carcinogen. In addition, methylene chloride and other volatile halogenated compounds are environmentally undesirable due to their suspected role in the destruction of the ozone layer. Paint strippers are commonly rinsed off substrates with water; contamination of groundwater by halogenated solvents is therefore a potential health risk.
N-methyl-2-pyrrolidone (NMP) is a preferred substitute for chlorinated solvents because of its effectiveness, low toxicity, biodegradability, and high flash point. N-methylpyrrolidone typically will not "lift" paint from a substrate as rapidly as methylene chloride, but NMP has a much lower vapor pressure, and thus NMP can be used at elevated temperatures or in a soak tank. Since NMP has a low evaporation rate, lifted coatings may be readily peeled from substrates many hours after lifting. In a methylene chloride-based formulation, the lifted film will generally readhere to the substrate if the coating is not mechanically removed soon after lifting occurs. Several applications of a methylene chloride-based formulation may be necessary to completely remove thick or multiple layer coatings due to the rapid rate of solvent evaporation, while a single application of an NMP-based formulation may suffice.
A deterrent to the use of N-methyl-2-pyrrolidone as the primary solvent in coating remover formulations is the relatively high cost of NMP. Blends of NMP with less expensive, less effective solvents have been developed that have performance approximately equivalent to that of pure NMP. For example, a low toxicity paint remover containing NMP and an aromatic hydrocarbon is described in U.S. Pat. No. 4,120,810. U.S. Pat. No. 4,749,510 teaches a solvent blend effective as a coating remover in which NMP, an aromatic hydrocarbon, and formic acid are combined with surfactants, thickeners, and corrosion inhibitors. NMP has also been blended with benzyl alcohol and aromatic naphtha to obtain a useful paint remover, as taught in U.S. Pat. No. 4,732,695. U.S. Statutory Invention Registration H300 describes NMP and ethanolamine mixtures which are particularly effective on thick epoxy coatings. A paint stripper composition containing predominantly oxo-hexyl acetate and cyclohexanone with a minor proportion of NMP is disclosed in U.S. Pat. No. 4,666,626. A blend of NMP, alkanolamine, and an alkali or alkaline earth metal base is effective in removing paint from substrates, as shown in U.S. Pat. No. 4,276,186. U.S. Pat. No. 4,085,059 teaches a foam-type coating remover containing NMP and a water-based carrier.
N-methyl-2-pyrrolidone is clearly a preferred solvent for paint-stripping applications due to its effectiveness, low volatility, low toxicity, and biodegradability. However there is a need for inexpensive compositions comprised of a minimum amount of toxic and/or volatile substances that maintain the desirable performance characteristics of NMP. Biodegradable compositions that have little to no negative impact on the environment are also needed. In addition, there is a need for compositions derived primarily from renewable resources, such as plants and animals, rather than nonrenewable resources, such as petrochemicals.